1. Field of the Invention
This invention relates to helicopters in which in-plane vibrations of the rotor are transmitted to the helicopter fuselage, resulting in undesirable levels of vibration in the pilot and passenger compartments. More particularly this invention relates to improvements in bifilar absorbers carried by the helicopter rotor for rotation therewith.
2. Description of the Prior Art
U.S. Pat. No. 3,540,809, issued Nov. 17, 1970 to W. F. Paul et al, shows a helicopter equipped with bifilar absorbers. In the Paul et al patent the bifilar absorbers have a pendulous, or counterweight, element at the end of an arm projecting from the rotor hub in a plane normal to the axis of rotation of the rotor. The counterweight of each absorber is connected to its supporting arm by tuning pins which pass through enlarged apertures in the supporting arm and the counterweight of the absorber. These provide a rolling pendulous and vibration absorbing motion between the counterweight and its supporting arm. In a bifilar absorber excessive internal friction between the counterweight and its supporting structure can completely destroy absorber efficiency and, to prevent frictional face-to-face contact between the sides of the counterweight and the adjacent surfaces of its supporting arm, tapered washers are provided in the Paul et al patent between these confronting faces in an effort to reduce internal frictional damping. While these washers proved helpful, there remained too much frictional damping for satisfactory comfort of occupants of the helicopter.